The present invention relates to a valve device, equipped with a narrowed section which supplies a device with seal-gas.
When conveying aggressive gases with pumps there exists the problem that these gases enter into the motor chamber, bearing chamber or similar chambers where they give rise to corrosion. For the purpose of avoiding this problem it is known to continuously admit a seal-gas (inert gas, preferably nitrogen) into the endangered chambers at a pressure which is higher than the pressure of the gas being conveyed. Said seal-gas flows through the endangered chambers and prevents the entry of the detrimental gases.
From DE-A-2408256, for example, a turbomolecular vacuum pump having a motor chamber and a bearing chamber is known, into which a seal-gas is continuously admitted to protect the motor and the bearings. Through this means a significantly extended service life of the pump is attained. The chambers in need of protection detailed are supplied via valve devices (seal-gas valves) equipped with a narrowed section which are linked to a gas reservoir and where said valve devices shall maintain the desired seal-gas flow at a level between 0.2 and 1.2 mbar l/s, for example. Valve devices of this kind with an orifice as the narrowed section require very small orifice diameters, so that they will be prone to blockages. Moreover, their throughput is linearly dependent on the inlet pressure. When designing the narrowed section by way of a capillary the choice of greater diameters is possible; however, throughput increases according to the square of the inlet pressure. Finally it is known to employ control valves. However, at the low throughputs required here, these offer inferior control characteristics. Moreover, their operation is also dependent on the inlet pressure. The cause for variations in the inlet pressure is not only a gas reservoir being depleted; they will also occur if a multitude of chambers in need of a seal-gas supplyxe2x80x94as common in modern vacuum systems serving, for example, the production of semiconductorsxe2x80x94are connected to common gas reservoir drawing different quantities of seal-gas at different times.
It is the task of the present invention to create a valve device of the aforementioned kind which is cost-effective and which supplies a constant seal-gas flow over a wide range of inlet pressures.
This task is solved through the present invention by the characteristic features of the patent claims.
The pressure reducer positioned upstream of the narrowed section has the task of reducing the inlet pressure which for commonly employed seal-gas reservoirs may range up to 25 bar, to a fixed value of 0.2 to 2 bar, for example. As long as the pressure in the seal-gas reservoir does not drop below a fixed pressure level, the difference between the pressures ahead and after the narrowed section remains constant, i.e. the valve device according to the present invention supplies a constant seal-gas flow across a wide range of inlet pressures.
The narrowed section may be designed by way of a capillary or an orifice in a manner which is basically known. The design by way of a capillary is to be preferred so as to render the seal-gas valve less sensitive to contamination. This may also or additionally be attained by a filter positioned upstream of the narrowed section, between pressure reducer and narrowed section, for example.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.